Cancer is the second most common cause of death in the U.S., exceeded only by heart disease, accounting for nearly 1 of every 4 deaths. During their lifetime, 1 in 8 American women will develop breast cancer. The American Cancer Society estimates that 232,670 new cases of invasive breast cancer will be diagnosed among women in the U.S. during 2014; about 2,360 new cases are expected in men. An urgent need exists for targeted, safe breast cancer therapeutics, particularly for refractive disease.